In recent years, there has been an increasing demand to improve fuel efficiency of gasoline engines in automobiles. Cylinder injection engines that inject fuel directly into a combustion chamber and ignite a mixture of injected fuel and intake air with a spark plug to cause an explosion have become popular as an engine with high fuel efficiency. However, in cylinder injection engines, the fuel tends to adhere to the inside of the combustion chamber, making it necessary to suppress particle matter (PM) that is generated by incomplete combustion of the fuel adhered to the lower temperature wall. To solve this problem and to develop direct injection engines with low fuel consumption and low emissions, it is essential to optimize combustion inside the combustion chamber.
There are various driving conditions involved in the driving of an automobile such as high load driving, low load driving, and cold start. To optimize combustion, it is important to create an optimum mixture of fuel spray injected into the engine cylinder and air according to the driving conditions. A promising method for optimizing the fuel spray includes variable spraying which changes the length (penetration) of the fuel spray. Since the environment inside the combustion chamber differs depending on the driving condition, for example, to obtain a large output during high load driving, homogeneous combustion, which distributes the fuel spray throughout the combustion chamber by increasing the penetration, is required. To reduce fuel usage during low load driving, stratified charge combustion, which creates a fuel rich region near the spark plug by decreasing the penetration, is required. There is thus a need to provide a fuel injector that optimizes the shape of the fuel spray, and a controller of the fuel injector.
Additionally, since the fuel is injected inside a small combustion chamber in cylinder injection engines, the fuel tends to adhere, for example, to the piston and the inside of the combustion chamber. The fuel that adheres to the wall can be reduced by quickly vaporizing the fuel. Thus, in cylinder injection engines, fuel injection pressure is increased to promote atomization of the fuel spray. However, when the fuel injection pressure is set high, injection velocity increases and penetration tends to increase. Thus, from the point of view of reducing PM emission levels, there is an increasing demand particularly to reduce penetration.
For example, PTL 1 describes a fuel injector that is capable of changing the penetration of fuel injection by controlling a lift amount (movement amount) of a valve body of the fuel injector. In the fuel injector described in PTL 1, the valve body can be set to a plurality of lift amounts of a large lift amount and a small lift amount. The valve body that opens and closes injection holes is provided with protrusions in portions facing each injection hole, and the fuel is caused to go around the protrusions and flow into the injection holes from lateral portions and downstream portions of the injection holes. This gives a swirl component to the fuel injected from the injection holes so that the penetration is controlled to be reduced in the small lift amount. In the large lift amount, a swirl flow is not generated and the penetration is increased. Thus, the penetration can be changed according to the lift amount.